1. Field of the Invention
The field of art to which this invention pertains is solid-bed adsorptive separation. More specifically, the invention relates to an improved process for separating sucrose from thick juice.
2. Prior Art
Sucrose, which is a common form of sugar, is widely used in the food industry. The usual source for this compound is found in the juice of sugar cane, sugar beets and other sucrose-containing materials, known as "thick juice". The usual method of obtaining pure sucrose is to first recover a portion of it by crystallization from the thick juice, and then recover as much as possible of the sucrose remaining in the mother liquors, which are generally termed "molasses," which will still contain a relatively large amount of sucrose along with other sugars such as glucose, fructose, raffinose, etc. The latter compounds along with salts, amino acids, betaine, pyrollidone, carboxylic acid, etc., constitute crystallization inhibitors which make the recovery of the remaining sucrose difficult to accomplish and thus make the recovery of the sucrose no longer economically practical. In addition, the impurities which are present impart a taste to the molasses which renders the same inedible for human consumption.
Sugar beet molasses may contain approximately 50% sucrose and, therefore, it is highly desirable to extract this sucrose from the aforesaid molasses. Inasmuch as hereinbefore set forth, the molasses is bitter in human taste, the residual molasses it used in animal feed or as a fertilizer, and therefore a relatively low sucrose content is an acceptable feature of the molasses. At the present time there are only a few methods for extracting the sucrose present in molasses from the compounds of the type hereinbefore set forth. One such process which is utilized is the Steffan process in which the beet molasses is diluted to about 20% solids, refrigerated, and treated with a calcium compound such as calcium oxide. This results in the reaction of the sucrose present with the calcium oxide to form tricalcium sucrate which is an insoluble granular precipitate. This precipitate can then be removed from the diluted molasses solution by filtration followed by washing, to remove adhering impurities. The tricalcium sucrate is returned to the beet processing operation by adding to the incoming hot beet juice. Under such conditions, the tricalcium sucrate decomposes, releasing the sucrose to solution so that the calcium oxide has acted as a purification agent. However, a disadvantage which is inherent in the process is that certain impurities are recycled, particularly raffinose, which is a trihydrate material. With the continual recycling of the tricalcium sucrate, the amount of raffinose present begins to accumulate and, as hereinbefore discussed, will retard the desired crystallization of the sucrose, thus making it necessary to discard a certain amount of circulating molasses from time to time.
In addition to the Steffan process, it is also possible to separate sucrose from molasses by utilizing non-continuous chromatographic procedures which employ ion exchange resins to isolate sucrose from the molasses. The processes which effect this separation employ a strong acid, polystyrene ion exchange resin in the alkaline or alkaline earth form and typically are as described by H. J. HONGISTO (Technical Department, Finnish Sugar Company Ltd., Kantvik, Finland), Chromatographic Separation of Sugar Solutions; The Finsugar Molasses Desugarization Process; paper presented to the 23rd Tech. Conf., British Sugar Comp. Ltd., 1976; and by Dr. MOHAMMAD MUNIR (Central Laboratory, Suddeutsche Zucker AG., 6719 Obrigheim 5, Wormser Str. 1, Germany), "Molasses Sugar Recovery by Liquid Distribution Chromatography;" the International Sugar Journal, 1976, 78, 100-106. Other processes for separating components of molasses using ion exchange resins are as described in U.S. Pat. Nos. 4,101,338; 4,046,590; 3,975,205; and 3,884,714. However, none of the above procedures utilizing ion exchange resins achieves efficient separation of the sucrose, even though high purity can be obtained, primarily because the ion exchange resin is inefficient in separating sucrose from betaine. A further disadvantage relating to the use of ion exchange resins is that they require periodic backflushing and regeneration.
Attempts heretofore made to use zeolitic material as an adsorbent selective for sucrose were deemed successful only where it could be tolerated that certain other components of molasses such as raffinose and colored bodies would be adsorbed with the sucrose and be part of the sucrose product extract stream.
It has now been discovered that sucrose may be separated and recovered directly from thick juice by an adsorption-desorption technique utilizing, as the adsorbent therefor, a certain new zeolitic adsorbent.